I had to go with Aldynes. R-Type and Parodius are pretty close, and Aeroblasters is great 2-player fun, but Aldynes just has this original, hardcore, gritty feel to it that I love. It almost feels like a spiritual precursor to Gate Of Thunder and some of the same people worked on both games, iirc. R-Type flickers a bit too much so that it affects the gameplay a little bit, and Parodius and Air Zonk are awesome but I've never been a big fan of cute-em-ups. The no-gravity levels in Aeroblasters kind of drag it down, for me.